Stabilized gelatino silver halide photographic emulsion



Patented Dec. 19, 1950 UNITED, STATES PATENT OFFICE STABILIZED GELATINO' SILVER HALIDE PHOTOGRAPHIC' EMULSIGN.

Dennis John Thomas Howe, Barnet, England, assignor to Elliott & Sons Limited, Bar'nct, England, aco'mpany of Great Britainv No: Drawing. Application J nly 15,1947, Serial No; 761,159. In Great Britain July 25,1946

8 Claims.

encyior the maximum-density to be' reduced and 1 the image to assume a bronzed appearance. This is particularly noticeable in, the case of emulsions composed principally of gelatino silver chloride.

' Further, whena photographic emulsion is kept 1 for some time, whether in the uncoated state or in the form of coated photographic material, itsi photographic properties tend to deteriorate, this deterioration being accelerated by humid and warm conditions. The most noticeable form of deterioration is the increase; in fog value, particularly with the fast negative type of emulsion. The fog value of positive emulsions also has a tendency to increase on keeping, and with these emulsions continued keeping eventually leads to the production of images of poor colour, and to staining on extended development.

Compounds areknown which, when added to sin-emulsion, will cou'nteractone or other'of these deficiencies; For-instance, compounds are known which stabilize an emulsion against the increase of fog value. Amongthese are the organic cornpoundswhich form silver salts, the solubility of which at t8- C. does not surpass that of silver chloride; A specificcompound of this type is the mono mercapto triazcle; n-ethyl thiotriazole. But while they may be effective as stabilizers these and other compounds cause a serious reduction in speed of the photographic emulsion in which they are applied.

In" accordance with the present invention it has. been found that the deterioration of the emulsion due to ageing can be reduced, parti'cul'arly with regard to increase in fog value, and in addition the quality of the image and the maximum density, particularly after hot glazing, can be improved, b the use of a substituted dithiourazole- Accordingto one form of the present invention, therefore, a gelatinosilver halide emulsion may beimproved with. regard to stabilization for the formation of fog by adding to the material, at any stage, not. later than development, a small quantityof a substituted dithiourazole.

free s ut .di hiq erel s. Whi s are of use as improversor stabilizers have the general molecular formula:

where R1 and: R2 are: either, hydrogen or alkyl; aryl or aralkyimolecular:groupsbut are not both hydrogen. This formula. is. shown in, the keto form; but all tau'tomeric; forms. are included in the scope of:th,ei invention. The dienol form may also be named 3z5=d imercapto 1.2.4 .triazole. 5 Examples, of: compounds having, this general formula are: 1 phenyl dithiourazole; i phenyl dithiourazole',

2o methyl" dithiouraz'ole,

1' ethyl dithioura'zolei 4 substituted; dithiourazoles may be prepared by treating the corresponding substituted hydra-Z0. dithiocarbonamide with hydrochloric acid or caustic. soda. solution as described in fBerichteder Deutschen Chemischen Gesel'lschaiit, 192 2,-vo1. l, page/35,2 (55th year).

The; preparation of 1 phenyl dithi'ourazole is described in, Berichte, der Deutschen Chemischen so Gesellschaft, 1,904, vol. 1, page 184, (37th year) The substituted dithiourazoles or dithiourazole compounds as described: above give rise to a smaller reduction in speed than do compounds hitherto proposed for similar purposes.

Gelatino silver chloride emulsions containing a dithioura-zole compound are capable of producing. a higher. maximum: black after hot glazing than does such; an emulsion. containing, one of the compounds previously proposed for this 40 purposetor example, a, monomercapto triazolel.

While this invention; is independent of any particular theory itissuggestedl that this is possibly due to the presence of two potential reactive groupsin the, dithiourazole compound compared with, the. one reactive group in the previously pro,-

posed compounds,

The dithiourazolev compound, may be incorporated in the emulsion as an addition,conveni'entls in the form. of a solution of the free substance or one of its salts, during. or subsequent to. the

preparationof the emulsion. Other methods of bringing the compound inoperative contact with the emulsion may be used such as including it in the subcoat, supercoat, backing layer; a filter layer, or in the wrapping material.

As mentioned above the dithiourazole compounds do not cause so great a reduction in speed as that which results from the use of some of the other compounds hitherto proposed. This is particularly the case with certain substituted dithiourazoles such as the l or 4 phenyl dithiourazole where the quantity required for use as an improver has a practically negligible effect on speed and contrast. However, when used in the free state, certain other dithiourazole compounds, may cause a slight alteration in the photographic properties of the emulsion. To minimise any such alteration of'properties the addition should preferably be made after the final digestion period rather than at an earlier stage of emulsion manufacture. If stabilization against fog is the improvement required, then obviously the dithiourazole compound must be in operative contact with the emulsion during keeping and before development.

Naturally, it is an advantage for the manufacturer to be able to incorporate the dithiourazole compounds in the photographic material, and should he wish to use a dithiourazole compound which in its free state would have an adverse effeet on the emulsion, this may be accomplished without this adverse effect by using it in the form of a metal salt which is substantially water insoluble but decomposable by treatment of the photographic element in a processing bath subsequent to development. The silver salt of a dithiourazole compound is most useful when added to the emulsion or to a layer in contact with the emulsion. Other metal salts may be used, including thallous, ferric, and copper salts.

It is advisable for the metal salt to be in a fine state of subdivision in the layer in which it is incorporated. A convenient method of achievin this is to deposit the metal salt in situ in the colloidal medium in which it is dispersed, by the double decomposition of a water soluble metal salt and a water soluble salt of the dithiourazole compound in gelatine solution.

.The quantity of the dithiourazole compound or its soluble salt employed varies with the purpose for which it is used, and with the method adopted for bringing it into operative contact with the emulsion. For direct addition, from 1 cc. to 40 cc. of /1000 solution per litre of emulsion is suitable if the improvement required is stabilization, particularly of a fast negative emulsion, and it is advisable to select a compound for use which has little or no detrimental effect on the properties of the emulsion such, for example, as an aryl substituted dithiourazole.

To improve the maximum density of image produced in a positive emulsion the quantity suitable for a litre of emulsion is from 1 cc. to '70 cc. of /1000 solution. The solution may be in water or in a water miscible organic solvent which does not have a detrimental efiect on the emulsion. If the additions are made to colloids which are to be coated adjacent to the emulsion layer, then higher quantities are preferable, approximately twice the quantity that would be used for a similar quantity of emulsion being required. These quantities are not given to limit the invention but merely as an indication of the order of the quantity of the compound to be used to give the best results.

Usually smaller quantities give less marked improvements, while higher quantities produce no additional improvement and moreover tend to affect the photographic properties adversely to a greater extent.

However, with the nonsoluble salts of the dithiourazole compounds, much greater quantities may be used without detriment to the photographic properties, whether the salts are included in the emulsion or in adjacent layers.

The following examples illustrate the invention, but it will be appreciated that invention is not limited to the specific materials, quantities, methods or other features described therein.

Example 1 Three separate l-lb. quantities of a negative gelatino silver iodo bromide emulsion having a silver content equivalent to 20 gms. silver nitrate per l-lb. of emulsion were taken and panchromatized. To one part was added the normal coating additions and it was coated on to glass plates (material A). The second quantity was coated after 13 cc. of /1000 spirit solution of 4-. phenyl 3.5 dithiourazole had been added (material B). The third quantity was coated after 13 cc. of /1000 spirit solution of 1 phenyl 3.5 dithiourazole had been similarly added (material C).

Fresh coated test portions of the material were exposed behind a density step wedge and processed, and the fog values of materials A, B and C were determined. Other test portions were kept at F. and at a relative humidity of 70% for two weeks. These materials were similarly tested and the fog values determined. The fog values were as follows:

After tWO Material gg gk weeks incubation Example 2 3-lbs. of a gelatino silver bromide positive (Bromide) emulsion were divided equally. One half was coated on to paper normally (material A), and the other half was likewise coated after addition of 20 cc. of /1000 aqueous solution of l phenyl 3.5 dithiourazole had been made to it (material D). When dry test samples of each of the coated materials were exposed behind a density step wedge, developed, fixed and glazed on a commercial hot glazing machine. Maximum density and speed were determined for each material. A sample of each material was incubated for two weeks at 110 F. at a relative humidity of 70% and the condition of material noted after development for 6 minutes in a standard MQ developer, at 18 C. with the following results:

There was no appreciable difference in speed and contrast between materials A and D.

Example 3 l /z-lbs. of gelatino silver chloride emulsion were coated in the normal manner on to paper (material A). To another l /2-lbs. of the same emulsion were added 12 cc. of 1000 spirit solution of 4 phenyl 3.5 dithiourazole and the emulsion Condition. of'incu- Maximum Material density after Pgfig 3 552 hot glazing ment p 1. 55 Slight yellow stain.

1.80 No stain.

1.75 No stain.

Example 4 This was performed to show the effect of varying the quantity of the improver. To l -lbs. quantities of a gelatino silver chloride emulsion were added various quantities of 4 phenyl 3.5 dithiourazole, and the emulsions were coated on to paper and tested as in Example 2, with the following results:

No. of cc. of

V1000 spirit Efiect on photographic properties 3 353 5 3 solution of of emulsion hot a improver 0 cc. l. 60 None l. 76 Very slight increase of emulsion toe... l. 80 Some loss of contrast 1. 87

Example 5 This was performed to compare the effect of a substituted dithiourazole in the emulsion with its efiect when included in a supercoat, and with the effect of a much larger quantity of its silver salt in the emulsion.

Material A was a standard Gaslight emulsion coated on to paper and coated with a standard gelatine supercoat.

Material B was as material A, but with cc. of 4 phenyl dithiourazole added per l /z-lbs. of emulsion.

Material C was as material A, but with 70 cc. of 4 phenyl dithiourazole per litre of supercoat.

Material D was as material A, but with an addition to the emulsion of the silver salt of 4 phenyl dithiourazole. This was prepared by adding the chemical equivalent of silver nitrate to 60 cc. of a l gelatine solution of 0.3 gm. of the sodium salt of l phenyl 3.5 dithiourazole.

The materials were tested as in Example 2, with the following results:

Maximum density after hot glazing wherein R1 and R2 are constituents selected from the following groups: hydrogen, alkyl, aryl and aralkyl, but are not both hydrogen.

2. A photographic material as claimed in claim 4 in which the said substance is present in the proportion of between 1 cc. and 70 cc. of /1000 solution of. the substance per litre of gelatino silver halide emulsion.

32 A photographic material as claimed in claim '6 which the 4 phenyl 3.5 dithiourazole is present in the proportion of between 1 cc. and 70 cc. of a /1000 solution thereof per litre of gelatino silver halide emulsion.

4. A photographic material which includes a gelatino silver halide emulsion and a substance having the following formula 40 wherein R1 and R2 are constituents selected from the following groups: hydrogen, alkyl, aryl and aralkyl but are not both hydrogen.

6. A photographic material which includes a gelatino silver halide emulsion and 4 phenyl 3.5 dithiourazole.

7. A photographic material which includes a support and a plurality of layers coated thereon, at least one of these layers comprising a gelatino silver halide emulsion, and at least one of these layers containing 4 phenyl 3.5 dithiourazole.

8. A photographic material which includes a gelatino silver halide emulsion layer in which is incorporated a compound selected from the group consisting of substituted dithiourazoles and the metal salts of substituted dithiourazoles wherein the substituted dithiourazole has the. formula:

wherein R1 and R2 are constituents selected from the following group: hydrogen, alkyl, aryl and aralkyl, but are not both hydrogen, and wherein the metal salts of substituted dithiourazole in accordance with said formulas are selected from the group consisting of silver, thallium, ferric iron and copper.

DENNIS JOHN THOMAS HOWE.

(References on following page) REFERENCES cI'T'Efi The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Jelley Nov. 3, 1925 Dieterle Dec. 29, 1936 Peterson July 18, 1944 Chilton Dec. 16, 1947 10 FOREIGN PATENTS Number Country Date 163,039 Switzerland Sept. 16, 1933 Great Britain Jan. 6, 1934 OTHER REFERENCES Berichte der deutschen Chem. Ges., 1895, vol. I, page 949; ibid., 1922, vol. I, page 352; ibid., 1904, vol. I, page 184. 

8. A PHTOGRAPHIC MATERIAL WHICH INCLUDES A GELATINO SILVER HALIDE EMULSION LAYER IN WHICH IS INCORPORATED A COMPOUND SELECTED FROM THE GROUP CONSISTING OF SUBSTITUTED DITHIOURAZOLES AND THE METAL SALTS OF SUBSTITUTED DITHIOURAZOLES WHEREIN TEH SUBSTITUTED DITHIOURAZOLE HAS THE FORMULA: 